The present invention relates to a two component chemically thermoset composite resin for use in composite manufacturing processes.
The styrene and solvent content of composite resins presently in use contribute to lost time in the work place as a result of precautions which must be taken for the safety of the workers due to emissions given off during the curing process. There has long been recognized a need to switch to a volatile organic compound (VOC) free composite resin. All VOC free composite resins, such as thermoplastic polyurethanes and epoxies, are either too expensive or do not exhibit the properties necessary for use in consumer products.
What is required is a VOC free composite resin that is less expensive to produce and yet has the necessary physical properties for use in composite manufacturing processes for consumer products.
According to the present invention there is provided a two component chemically thermoset composite resin which includes a solvent free polyisocyanate component and a solvent free polyol component. The solvent free polyisocyanate component is either an aromatic polyisocyanate, an aliphatic polyisocyanate or a blend of both. The solvent free polyol component is either a polyether polyol, a polyester polyol or a blend of both. The polyisocyanate component and the polyol component are in relative proportions in accordance with an OH/NCO equivalent ratio for 1:1 to 1:2.
While fibre type and style determine the ultimate strength potential of a product, the matrix resin determines the actual level of properties realized through effective coupling and stress transfer efficiency. Among these properties are flexural strength, impact resistance, high temperature performance, corrosion resistance, dielectric properties, flammability and thermal conductivity. The composite resin, as described above, is a urethane based resin that eliminates the release of volatile organic compounds. In addition, it is capable of providing a range of desirable physical properties. The formulation of the composite resin can be adjusted to provide superior fire retarding characteristics. The formulation can similarly be adjusted to provide superior properties of toughness, impact resistance, weathering resistance, and chemical resistance. In particular, the formulation has a unique capacity for elongation, impact strength and flexibility. This enables composite products made from the composite resin to be receive screws and other rotatable fasteners, whereas products made from existing composite resins are comparatively brittle and tend to shatter when receiving a rotatable fastener.
The selection of particular, polyisocyanate components and particular polyol components is dictated by the physical properties that one is seeking in the composite resin and by economics. An aliphatic polyisocyanate has superior resistance to chemicals and ultra violet rays. It is, therefore, recommended that the aliphatic polyisocyanate be used to the exclusion of the aromatic polyisocyanate, if the best possible composite resin is desired. However, the aliphatic polyisocyanate is much more expensive that the aromatic polyisocyanate. In order to obtain a balance between physical properties and cost, it is, therefore, preferred that the polyisocyanate component be a blend of at least 15% by weight of an aliphatic polyisocyanate with the remainder an aromatic polyisocyanate. Of course, composite resin can use exclusively the aromatic polyisocyanate where resistance to chemicals and ultra violet rays is not of concern. In the polyol component, it is preferred that a polyether polyol be blended with a polyester polyol in order to obtain the best physical properties. The polyether polyol has desired flexibility, but has a low glass transition temperature and poor chemical resistance. It is, therefore, preferred that the polyol component include at least 10% by weight of a polyester polyol with the remainder being a polyether polyol. Of course, the polyether polyol can be used exclusively where maximum flexibility is desired, and neither glass transition temperature nor chemical resistance is of concern. Similarly, the polyester polyol can be used exclusively where flexibility is not required.
When selecting an aromatic polyisocyanate, beneficial results have been obtained with methylene di-p-phenylene isocyanate. Methylene di-p-phenylene isocyanate has been found to have good reactivity and the amount of methylene di-p-phenylene in the composite resin can be used to adjust curing times. Methylene di-p-phenylene, however, tends to be relatively high in viscosity and is a solid in the its pure chemical state. It is, therefore, preferred that the aromatic polyisocyanate also include polymethylene polyphenyl isocyanate. Polymethylene polyphenyl isocyanate has been found to give the composite resin more reactivity and rigidity. It is preferred that the aliphatic polyisocyanate include isophorone diisocyanate polymer, hexamethylene diisocyanate polymer or a blend of both. Hexamethylene diisocyanate polymer has superior chemical resistance and resistance to ultra violet rays, it is, therefore, recommended that hexamethylene diisocyanate polymer be used to the exclusion of isophorone diisocyanate polymer, if the best possible composite resin is desired. However, the hexamethylene diisocyantate is much more expensive that the isophorone diisocyanate polymer. In order to obtain a balance between physical properties and cost, it is, therefore, preferred that the aliphatic polyisocyanate be a blend of at least 15% by weight of hexamethylene diisocyanate polymer with the remainder being isophorone diisocyanate polymer. When selecting a polyester polyol, beneficial results have been obtained with a diethylene glycol-phthalic anhydride. Diethylene glycol-phthalic anhydride has been found to have relatively high glass transition temperature, high reactivity, low cost, and good chemical resistance. When selecting a polyether polyol, a selection should be made based upon whether more importance is placed upon curing time or glass transition temperature. Beneficial results have been obtained controlling curing times through the use of the following polyether polyols, arranged in order of curing time from fastest to slowest: polyoxyalkylene polyol, propoxylated glycerol, branched polyol with ester and ether groups, and amine initiated-hydroxyl terminated polyoxyalkylene polyol. The same polyether polyols have a different rank order when arranged in order of glass transition temperature from highest to lowest: propoxylated glycerol, amine initiated-hydroxyl terminated polyoxyalkylene polyol, polyoxyalkylene polyol, and branched polyol with ester and ether groups. It will appreciated that a compatible wetting agent is required. Beneficial results have been obtained through the use of a polymer of ethylene oxide as the wetting agent.
In most, if not all, applications fiber reinforcement is provided. Without limiting the scope of possible applications, such applications include: pultrusion, resin injection molding, resin transfer molding, and hand lay-up forming applications. There are a variety of fibers that are suitable for use as fiber reinforcement, including: glass, carbon, fiberglass, aramid, polyester, nylon, polyethylene, ceramic, boron, metal, and natural fibers.
In some applications, first retardant properties are either required or viewed as desirable. Even more beneficial results may be obtained when a fire retardant additive added to the composite resin. There are a number of suitable fire retardant additives, including: diammonium phosphate, alumina trihydrate, antimony trioxide, antimony silicon-oxide, zinc borate, barium metaborate, phosphate compounds, extended molybdates, calcium sulfate, and dehydrates.
In many applications, chemical resistant properties are required or viewed as being desirable. In such applications, an aliphatic polyisocyanate is selected that has chemical resistant properties. The particular aliphatic polyisocyanate selected will depend upon what chemical the composite resin is to be resistant to. Some of aliphatic polyisocyanates having chemical resistant properties include: isophorone diisocyanate polymer, hexamethylene diisocyanate polymer and 4,4xe2x80x2-methylenebis (cyclohexyl isocyanate).
More information about formulations for the composite resins will hereinafter be described.